If only we did interracial marriage that way, amirite?
I am 100% for extending the legal definition of "marriage" to include any 2 consenting adults, regardless of sex/gender/orientation/etc.
However, the fact is that if a state supreme court decides that based on their state constitution gay marriage can't be denied, voters can still simply change the constitution, as they have done in so many states in this country in the last few years.
So if we're looking for the institutionalization of gay marriage, imposing it on a hostile population only makes it more likely that gay marraige will be postponed for a longer time due to heat-of-the-moment constitutional referendums.
While it seems heartless to say that gays in state X shouldn't be allowed to marry because a majority of people there don't like them, the fact is that young people are much more in favor of gay marriage, so we just have to wait for older people to die before gay marriage will be politically acceptable in much broader swathes of the country. Trying to institute it too early could actually delay the process of institutionalizing gay marriage.